1. Field of the Invention
The present invention relates to a new liquid crystal element and a liquid crystal display apparatus that utilize a transition between two orientation states.
2. Description of the Background Art
Japanese Patent No. 2510150 (hereinafter referred to as “Patent Document 1”) discloses a liquid crystal display apparatus in which electro-optical properties are improved by twisting and orienting the liquid crystal molecules in a turning direction that is opposite to a turning direction regulated by a combination of the directions of an orientation process performed on each of a pair of substrates disposed facing each other. Further, Japanese Unexamined Patent Application Publication No. 2007-293278 (hereinafter referred to as “Patent Document 2”) discloses a liquid crystal element in which the strain inside a liquid crystal layer is increased by twisting and orienting the liquid crystal molecules in a turning direction (first turning direction) regulated by a combination of directions of an orientation process performed on each of a pair of substrates disposed facing each other, while adding a chiral agent twisted in a turning direction (second turning direction) opposite to the first turning direction, thereby decreasing the threshold voltage and making low voltage driving possible.
However, the liquid crystal display apparatus of Patent Document 1 described above has the disadvantage that the reversed twist orientation state is unstable and, although the reversed twist orientation state can be obtained by applying a relatively high voltage to the liquid crystal layer, the state transitions to a splayed twist state over time. Further, the liquid crystal element of Patent Document 2, while having the advantage of decreasing the threshold voltage as described above, has the disadvantage that the state quickly transitions to a splayed twist orientation state (in about a few seconds, for example) when the voltage is turned off, thereby conversely increasing the threshold voltage. Further, neither Patent Document 1 nor Patent Document 2 assumes positive utilization of the two splayed twist and reversed twist orientation states as an application for displays or the like. That is, there exists no disclosure or suggestion of a technical idea such as a driving method or configuration required to positively utilize bistability or the like.
Hence, the present inventors have been engaged in investigating a liquid crystal element of a new reverse twisted-nematic mode (hereinafter abbreviated as R-TN mode) that can resolve the disadvantages of the prior documents described above. For example, Japanese Unexamined Patent Application Publication No. 2011-203547 (hereinafter referred to as “Patent Document 3”) discloses a technique related to an R-TN mode liquid crystal element that is in a splayed twist orientation in the initial state, but stabilizes in a reversed twist orientation when a vertical electric field is applied one time.
Further, the present inventors have been engaged in investigating a liquid crystal display apparatus in which a plurality of liquid crystal elements is arranged and each liquid crystal element is individually driven using a switching element such as a thin film transistor, as an embodiment of a liquid crystal display apparatus that uses the R-TN mode liquid crystal element described above. Hence, a structural example of a switching element and an electrode for driving using a horizontal electric field is disclosed in Japanese Patent No. 4238877 (hereinafter referred to as “Patent Document 4”), for example. Nevertheless, the structure of the switching element and the electrode such as disclosed in this Patent Document 4 is not suitable for driving the new R-TN mode liquid crystal element according to the present inventors.
However, while the R-TN mode liquid crystal element disclosed in Patent Document 3 is capable of static image display utilizing the memory property thereof, basically one of the two orientation states is selectively used, making the element not suitable for optical control that supports half-tone displays and moving image displays. Further, in the R-TN mode liquid crystal element disclosed in Patent Document 3, the contrast ratio from the front is not significantly high, and thus further improvement of the contrast ratio has been desired.
It is therefore an object of the specific aspects according to the present invention to provide a liquid crystal element with a high contrast ratio that is capable of achieving both optical control that utilizes a memory property and optical control capable of supporting moving image displays and the like.
Further, another object of the specific aspects according to the present invention is to provide a liquid crystal display apparatus with a high contrast ratio that is capable of achieving both displays that utilize a memory property and moving image displays and the like.